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Using a clonal line of bovine parathyroid endothelial cells (BPE-1) we defined the presence on these cells of a histamine H2 receptor and characterized its pharmacological properties. Interaction of histamine with its receptor induced an increase of cAMP accumulation in a dose- and time-dependent fashion. This effect appears unique for parathyroid endothelial cells, in fact, clonal parathyroid epithelial cells did not exhibit a similar response. No effect of histamine was observed on BPE-1 cell proliferation.

Basal adenylate cyclase activity of thyroid plasma membranes obtained from six patients with Graves' disease was slightly but not significantly lower than normal (83.3 +/- 13.9 pmol cAMP/10 min/mg of protein versus 120.9 +/- 19.5 pmol cAMP/10 min/mg of protein). In five of these patients the adenylate cyclase activity was stimulated by bovine TSH with an apparent Km value similar to that of normal thyroid (3.1 +/- 0.5 X 10-9 M versus 3.4 +/- 0.6 X 10-9 M). The response to prostaglandin E2 was also normal. In the sixth patient adenylate cyclase activity was stimulated by prostaglandin E2 but not by bovine TSH. The distribution of basal adenylate cyclase activity in various gradient layers was studied in two TSH-responsive patients. A relative increase of this activity was found in the denser layer when compared to normal thyroid tissue. This could be the expression of an altered ratio between the protein and lipid components of the plasma membranes in patients with Graves' disease.